There are three main types of antiperspirant stick formulations: compressed powder sticks, gel sticks, and wax sticks. While each of these formulation types may have advantages in certain usage situations, each also has disadvantages. For example, compressed powder sticks are often brittle and hard, leaving a cosmetically-unacceptable powder on the skin upon application. Wax-based formulations can also yield cosmetically-unacceptable products due to such factors as hardness, greasiness, and stickiness. The opacity of such wax sticks and the residue created by their use may also be aesthetically undesirable.
Gel-based sticks have several advantages over both compressed powder and wax sticks. For example, the gel sticks tend to leave little or no residue or dust on the skin. Gel sticks also provide a vehicle which glides easily over the skin's surface resulting in very easy and comfortable application of the product.
Unfortunately, the formulation of antiperspirant compositions in the form of effective and stable gel sticks is difficult. The inclusion of antiperspirant actives in such compositions results in the final product having an acidic pH. Many of the gelling agents typically used in forming cosmetic gel sticks either do not form effective hard gels or tend to degrade under such acidic conditions. The products sometimes degrade in periods as short as one month or less. For example, dibenzylidene sorbitol (DBS) is a well-known gelling agent. See, for example, U.S. Pat. No. 4,154,816, Roehl et al., issued May 15, 1979; U.S. Pat. No. 4,816,261, Luebbe et al., issued Mar. 28, 1989; and U.S. Pat. No. 4,743,444, McCall, issued May 10, 1988. Unfortunately, when DBS is used as a gelling agent in an acidic environment, such as is required in an antiperspirant product, it tends to degrade rapidly, resulting in a product which has a short shelf life. Since typical commercial distribution channels for antiperspirant products require storage for relatively long periods of time in factories, warehouses, and retail outlets, sometimes at elevated temperatures, degradation of the gelling agent and the resulting short product shelf life is a significant disadvantage. See, for example, U.S. Pat. No. 4,518,582, Schamper et al., issued May 21, 1985. It, therefore, would be beneficial to identify a gelling agent which forms effective hard gels in an antiperspirant context, and is stable under the acidic conditions present in such products.
The effect that various substituents have upon the hydrolysis rates of some acetals and ketals is demonstrated in Kreevoy and Taft, J. Am. Chem. Soc., 77 5590-95 (1955).
Japanese Published Application 64-62377, Kao, published Mar. 8, 1989, describes fluorinated dibenzylidene polyhydric alcohol derivatives which are effective gelling agents for cosmetic compositions containing a wide range of organic solvents. These compounds are not disclosed for use in antiperspirant compositions.
U.S. Pat. 4,429,140, Murai et al., issued Jan. 31, 1984, discloses a method for producing DBS and its derivatives. Disclosed DBS derivatives include those where the benzene ring is substituted with from 1 to 3 lower alkyl groups, lower alkoxy groups, halogen atoms or nitro groups. Para-chloro dibenzylidene xylitol and para-methoxy DBS are specifically disclosed; meta-substituted DBS derivatives are not taught. There is no suggestion to use these compounds in antiperspirant compositions.
U.S. Pat. No. 4,371,645, Mahaffey, issued Feb. 1, 1983, describes plastic compositions which include DBS derivatives for improved transparency. These DBS derivatives must include a chlorine or bromine substituent in the meta and/or para positions and may also include lower alkyl, hydroxy, methoxy, mono- or dialkyl amino, or fluorine substituents. Di(para-chloro) DBS, di(para-fluoro) DBS, and di(para-methoxy) DBS are all specifically disclosed. These compounds are not taught for use in antiperspirant compositions.
European Patent Application 0286522, Roquette Freres, published Dec. 1, 1988, describes a process for making high purity alditol diacetals. Para-chloro DBS is disclosed. However, the use of such compounds in antiperspirant compositions is not suggested.
While the art teaches some DBS-type compounds derivatized with electron withdrawing groups, there is no teaching that such compounds must be derivatized at the meta position or of using such compounds in antiperspirant stick compositions. Further, there is no suggestion that such compounds, when used in the acidic environment of an antiperspirant stick formulation, would provide effective gels and long term stability. Finally, specific compounds, such as di(meta-fluoro) DBS and di(meta-chloro) DBS, are not suggested in the art.
The present invention provides very specific gelling agents which, when used in acidic antiperspirant stick formulations, provide good gel properties without the degradation problem which typically accompanies the use of DBS in antiperspirant sticks.